The invention relates to an optical device for converting a uniform light beam into an array of light spots for illuminating a periodic array.
A periodic array of illumination spots is required by several electrooptic devices. For example, two-dimensional optical logic arrays require uniform illumination of each optical gate in the array to provide power to the array. Some vertical cavity surface-emitting laser diode arrays are optically pumped, thus requiring a regular array of pump sources. In addition, in certain processors where clock skew currently limits the cycle time of the processor, a synchronous distribution of clock signals to electronic or optical logic elements would overcome that limitation.
There are currently several techniques for illuminating periodic arrays. One common method uses a diffraction grating to split a single beam into many diffraction orders. Since simple diffraction gratings do not produce a uniform set of illumination spots, specially designed gratings have been fabricated to produce a uniform spot array with high efficiency. However, there is a practical limit on the number of illumination spots obtainable by this method.
Arrays of microlenses have also been used to convert uniform illumination into a set of focussed spots. However, the light from a single microlens array is not uniform in amplitude or phase across each spot. Uniform illumination can be produced by using two planes of microlenses in a Galilean or Newtonian telescope configuration, but this is done at the expense of added complexity and additional alignment problems. Finally, phase contrast methods have also been used to convert phase masks into amplitude distributions. This system requires several additional optical elements as compared to the other described approaches and it places constraints on the fill factor achievable for the resultant image.